1. Field of the Invention
The present invention relates to compound semiconductor wafers produced by forming epitaxial layers in the ion beam deposition process or the cluster ion beam deposition process, which are low in cost and controlled in shape and can be made large in size and also can be applied to light-emitting diodes, solar cells, photo detectors, etc.
2. Description of the Prior Art
In the case of compound semiconductors, the band gap thereof can be freely controlled by changing the kinds of proportions of the component elements thereof. Therefore, if the compound semiconductors are used for forming light-emitting diodes, the resulting diodes can emit light at any wavelength in the range from red light to blue light. Besides, some kinds of the compound semiconductors are very high in electron mobility and therefore very useful as ultrahigh frequency devices. In addition, the compound semiconductors have many interesting characteristics as dielectrics, magnetic substances, etc., and therefore are attracting attention from various fields as promising electronic materials.
The wafers of the above-mentioned compound semiconductors are conventionally produced by the melt growth method, solution growth method, etc. Besides, in the case of a compound semiconductor, as GaP, having a high dissociation pressure at the melting point, the so-called LEC (Liquid Encapsulated Czochralski method) recently developed is used, in which pressure is applied to the liquid from above in order to prevent the escape of V-group elements.
However, when GaP wafers are to be produced by the above-mentioned LEC method, it is necessary to heat polycrystalline GaP to its melting point and also to confine the melt in an atmosphere having a high pressure higher than the dissociation pressure of the melt at the melting point thereof in order to prevent evaporation of volatile elements, as phosphorus. In this case, operations must be performed at high temperatures and pressures. As a result, a complicated production equipment and a number of complicated processes become necessary. Accordingly, the wafers thus produced are expensive. In addition, these wafers have many problems from the viewpoint of crystallinity. When actual devices, as GaP light-emitting diodes, are to be produced, it is necessary to additionally form epitaxial growth layers on the above-mentioned wafers by the liquid or vapor growth method. Consequently, the devices thus produced are very high in cost.
Besides, compound semiconductor wafers produced by the liquid or vapor growth method also have problems from the viewpoint of crystallinity. In addition, the production equipment thereof is very complicated and expensive, and the production process thereof is also very complicated. As a result, the wafers thus produced become very expensive.
The above-mentioned LEC method and the solution growth method require polycrystalline compound semiconductors as the starting material for producing the wafers. In other words, the above methods have disadvantage in that they cannot produce monocrystalline compound semiconductors directly from the component elements.
In addition, the wafers produced by the above-mentioned production methods are uncontrolled or non-uniform in shape. For instance, truly circular wafers cannot be produced unlike in the case of silicon or germanium wafers produced by the pulling method, and therefore complicated handling operations are required for splitting the wafers into chips when devices are to be produced. As a result, automation of the production process cannot be easily achieved.